Integrated circuit chip wiring is divided into roughly four physical design phases: global wiring, detailed wiring, rip/reroute and finally interactive wiring. Global routing divides the chip into a rectangular global cell grid, where each column or row of cells is referred to as a bay. The number of bays and size of each bay is defined ahead of time, depending on the overall chip size. The global router looks at the various connections that must cross vertical and horizontal bay boundaries and assigns the routes based on supply and demand at a given crossing. Thus the connections in a given net end up being assigned to various vertical and horizontal bays and this becomes the input to the detailed router.
The Job of the detailed router is to route each bay in succession using the rough coordinates suggested by the global router. The connections inside a bay are well defined. Two passes are performed in the post-global phases: first the vertical bays; then the horizontal bays. Prior to this invention, all of the bays in the post-global phases were wired in a serial fashion and thus the process was relatively slow.